1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device whose isolation regions are flattened by means of chemical-and-mechanical polishing (hereinafter called simply xe2x80x9cCMPxe2x80x9d) as well as to a method of manufacturing the semiconductor device.
2. Description of the Background Art
FIG. 6 is a plan view showing a semiconductor wafer processed according to a conventional manufacturing method. As shown in FIG. 6, reference numeral 10 designates an isolation region formed by means of the trench isolation technique. Reference numeral 12 designates active regions separated by the isolation region 10. FIG. 7 is a cross-sectional view for describing the conventional trench isolation technique for forming on a semiconductor wafer the isolation region 10 shown in FIG. 6.
According to the trench isolation technique, a nitride film 16 is formed on a silicon layer 14 of the semiconductor wafer. Next, a trench 18 which is to become the isolation region 10 is formed in the silicon layer 14 and the nitride film 16. Next, an oxide is deposited over the entire surface of a semiconductor wafer so as to be embedded in the trench 18. Finally, undesired oxides are removed by means of CMP while the nitride film 16 is used as a stopper film. As a consequence, oxides remain only within the trench 18, thus forming the isolation region 10 which separates the isolation regions 12.
A CMP operation employed in the course of forming the isolation region 10 is performed on condition that an oxide film is abraded at a higher rate than is a nitride film. For this reason, a so-called dishing phenomenon arises in the isolation region 10 when the isolation region 10 occupies a comparatively large area of the semiconductor wafer, as shown in FIG. 7.
If a dishing phenomenon arises in a specific isolation region 10, intensive force arises in the active regions 12 adjoining the isolation region 10. Consequently, the nitride film 16 covering the active regions 12 that undergo intensive stress is abraded much more than is the nitride film 16 covering other regions. As mentioned above, in a case where a large isolation region 10 is present, the structure of a conventional semiconductor device and the conventional trench isolation technique pose a problem of an active region being apt to vary in its finished state.
The present invention has been conceived to solve the foregoing problem and is aimed at providing a semiconductor device which prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present.
The present invention is also aimed at providing a method of manufacturing a semiconductor device, which device prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present.
The above objects of the present invention are achieved by . . . . The . . . includes.
The above objects of the present invention are achieved by . . . . The . . . includes.